Protective arrangement for high voltage systems



J. JONAS Aug. 17,1943.

PROTECTIVE ARRANGEMENT FOR HIGH VOLTAGE SYSTEMS Filed March 25, 19413mm.- W 2 PM f 5% Patented Aug. 17, 1943 l u Jones 2 in h sweaters. asiiii r it Aktiengesellscha-ft Brown, Bovcri & Cie., "Baden,

. sameness ifipl'ilicatioh March 25, 1941, Serial 'No'. 385190 InSwitzerland April 10, 1940 The invention relates to high voltage polphase electric transmission systems and particularly to means forprotecting such-systems from the effects of earth faults and shortcircuits.

It is known that polyph'a'se high voltage lines can be protected againstthe effects of earth faults by earthing the neutral point of a windingconnected to the line by means of an inductance which is at leastapproximately in resonance with the capacity of the network to earth.Such coils extinguish the earth fault arc and enable the line to remainin service with a single phaseto-earth fault. They have, however, thedisadvantage that in the event ofan earth fault (and withan'unsymm'etri'cal network even in normal service) the voltage of theline to earth becomes greatly displaced so that the insulators must bedimensioned for considerably higher voltages and in consequence the testvoltage must therefore also be higher. With high voltage lines theVoltage displacement of the line relative to the earth results inunecon'omical conditions because with such high operating voltages it isdifficult to obtain a durable insulation even for the simple phasevoltage. Also the arc extinction coil does not provide protectionagainst a double pole earth fault or a short circuit between two lineconductors. For this reason high voltage lines are provided with adirectly earthed neutral point so that the conductors and appa'-' ratushave only to be insulated against the earth forthe simple phase voltage.Protection against earth faults and short circuits between phases isprovided by means of high-speed switching devices which are located asusual on the high voltage side of the line. Upon the occurrence of anearth fault or short circuit on one or more of the network conductorsthe switching devices disconnect the affected conductor as soon aspossible. In order to avoid a service interruption of long duration theconductor on which the fault occurs is switched out and in at shortintervals and the conductor is only then finally disconnected when it isshown that a disconnection of short duration is not sufiicient toeliminate the cause of the fault. The disadvantage of this protectivedeviceis, however, that-the switch apparatus is subjected to a highvoltage and must therefore be very well insulated, .thus increasing thecost ofthe installation and complicating the operationof the system. l

The object of the present invention is therefore to provide an improvedprotective arrangement which does not possess the aforementioneddisadvantages. This is achieved according to the invention by producingthe vdltages of the individual "phases of the high voltage line inmutually independent magnetic circuits of a transformer arrangement;each winding branchbf the low voltage side or the'transforme'rarran'ge'ment being provided with a quick-acting switchingdevice which operates upon the occurrence or an earth fault or short-circuit in the high voltage conductor associated with this particularphase and disconnects the conductor "or the associated winding branch'on the low voltage side at least temporarily. The circuit breakers forthis high speed interruption thus only need to be 'dime'n sioned for alow voltage so that standard designs can be employed. i

Two constructional examples of the invention are illustrateddiagrammatically inFlg's. l and? of the accompanying drawing.

'InFi'gs". 1 and 2 the three-phase high voltage system l1, l2, Z3 issupplied from a transformer arrangement the primary windings an, in, m"of which are 'connectedto thelow voltage supply network I01, 702, 103.This supply networkcan .also be replaced by the bus bars of a generator.The secondary windings or, 112, (13 of the transformer arrangement arestar connected the star point being directly earthen. There are nocircuit breakers located on the high voltageside which have to beoperated under voltage. The circuit breakers 21, e2, '23 on the highvoltage side shown in Fig. 2 and connected in parallel with thesecondary windings 111, :12, (1'3 must only have a sufficient insulationclearance but do not need to in: terrupt any. power: Their function isreferred 2 to later on; they can often be dispensed with or located onthe low voltage side as shown in Fig. 1. With the arrangements shown inFigs. 1 and '2 the service circuit breakers sr,sz, s3 are'locatedinserieswith the primary winding branches pr, 122, 23 respectively and in"such a manner, that when there is a disconnected winding either; in thedelta system of connections shown in Fig. tor the star system ofconnections shown in Fig". 2 a two-phase three-wine operation, with starconnection by means of the neutral wire n, is always possible. Themagnetic coupling between the primary side carrying the low voltage andthe secondary side of the transformer arrangement connected to thetransmission line is constructed in such a manner that arn'a gneticcoupling between individual passes does not that. "A three: phase transformer with stieost the additional core arranged tosuit can thus beused. it is, however, preferable to employ three separate single-phasetransformers,

In order to explain the manner in which this protective system operatesit is assumed that for instance the conductor 11 of the transmissionline has an earth fault. The circuit breakers s1,

phases, the circuit breakers s1, s2, 83 can be.

opened. In this case, circuit breaker s1 is opened by the-action ofrelay 11, while breakers s2 and s3 remain closed. The primary winding 1mis disconnected and the conductor 11 is made dead.

If there is only an earth fault are this will be i extinguished when thecircuit breaker s1 opens and the conductor h can be put under voltageagainby closing the circuit breaker s1. ,If the or 'ashort circuit onthehigh voltage conductor corresponding to such winding.

2. In a high voltage polyphase electric transmission system including aconductor for each phase, transformer means for supplying the voltagesof the individual phases of the high voltage j line, said transformermeans having mutually conductor Z1 has, however, a permanent earth faultthe transmission of energy will not be interrupted by the opening of thecircuit breaker 31 because both of the conductors Z2, Z3 whichare notafiected by thevfault take over by way of the earth conductor the wholeofthe power to be transmitted--andiin sucha manner that a twophase.three-wire. service:results, the earth bein used as the returnconductor. Upon opening the circuit breaker 81, the circuit breaker 21is closed, whereby the primary winding 101 is shunted and thereby thebuilding up of an excessive voltage in the faulty conductor Z1 isprevented so that the latter canbe utilized for the transmission ofpower. Theidefective part'of the line can thus be. repaired withoutv anyinterruption in service. I V

The conditions are similar if instead of a single phase earth fault atwo-phase earth fault occurs. If for instance both conductors Z1 and 12have an earth fault simultaneously both earth fault arcsare extinguishedby opening the circuitbreakers siand $2 on the primary side.

* When there is a" two-phase permanent earth independent magneticcircuits for each phase and the low voltage windings of said transformermeans beingconnected in delta, and a high speed circuit breaker inseries with eachlow voltage winding in the low voltage supply linethereto and means to open said breakerin response to an earth fault or ashort circuit on the high voltage conductor' corresponding to suchwinding. 7

3. In a high voltage polyphase electric transmission system including aconductor for each phase, transformer means for supplying the voltagesof the individual phases of the high voltage line, said transformermeans havingmutually independent magnetic circuits for each phase andthe low voltage windings of said transformer means being stareconnectedwith a neutral conductor connected to the star-point, anda high speedcircuitbreaker in series with each .loW voltage winding in the lowvoltage supply line thereto and means to open said breaker in responseto an earth fault or a short circuit on the high voltage'conductorcorresponding to such winding. I 5 I 4. In a high voltage. polyphaseelectric transmission system including aconductor for each phase,transformer means for supplying the voltages of the individual phases ofthe high voltage line, said transformer means having mutuallyindependent magnetic circuits for each phase and each low voltagewinding of said transformer means including a high speed circuit breakerin the low voltage supply-line thereto, means cuitsare, however,comparatively rare; Single- A special advantage of th protectivearrangement described is that the circuit breakers which have to beoperated in service are located on the low voltage side so that it ispossible to extinguish an earth fault or short-circuit arc by repeatedopening and clcsing of the circuit breakers s as long as there is not apermanent earth fault or short circuit. With protective 'arrangements'ofthis kind it is of. course essential to ensure that on both sides of thetransmission line the individual phases are not magneticallyinterlinked.

I claim; r

1. In a high voltagepolyphase electric transmission system including aconductor for each phase, transformer means for supplying th voltto opensaid breaker in response to an earth fault or a short circuit on thehigh voltage'conductor correspondingto such winding, switch meansadapted to short circuit each of the primary windings of saidtransformer means, and means to close said switch means upon theoccurrence of an earth fault on the high voltage conductor'correspondingto such winding.

5. In a high voltage polyphase electric..transmission system includingaconductor for each phase, a separate singlephase transformer 'forsupplying the, voltage of eachof' the individual phases of the highvoltage line, each low voltage winding. of said transformers including'a high speed circuit breaker in'the low voltage'supply line thereto andmeans to open said breaker in response to an earth fault or a shortcircuit on the high voltage conductor corresponding to such winding, 1

6.In,a.high voltage polyphase electric transmission system including aconductor for each phase,,transformer means for supplying the voltagesof the individual phases of the high voltage line,fsaid transformermeans having mutually ages of the individual phases of the high voltageline, said transformer mean having mutually independentmagnetic circuitsfor each phase and a each low voltage winding of said; transformer meansincluding a high speed circuit breaker in the low voltage supply linethereto and means to open said breaker in response to an earth fault

